<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html lang="en" dir="ltr" class="client-nojs">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Struct and union initialization - cppreference.com</title>
<meta charset="UTF-8">
<meta name="generator" content="MediaWiki 1.21.2">


<link rel="shortcut icon" href="../../../favicon.ico">



<link rel="stylesheet" href="../../../common/ext.css">
<meta name="ResourceLoaderDynamicStyles" content="">
<link rel="stylesheet" href="../../../common/site_modules.css">
<style>a:lang(ar),a:lang(ckb),a:lang(fa),a:lang(kk-arab),a:lang(mzn),a:lang(ps),a:lang(ur){text-decoration:none}#toc{display:none}.editsection{display:none}
/* cache key: mwiki1-mwiki_en_:resourceloader:filter:minify-css:7:472787eddcf4605d11de8c7ef047234f */</style>

<script src="../../../common/startup_scripts.js"></script>
<script>if(window.mw){
mw.config.set({"wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"c/language/struct_initialization","wgTitle":"c/language/struct initialization","wgCurRevisionId":79096,"wgArticleId":13916,"wgIsArticle":true,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["Todo with reason"],"wgBreakFrames":false,"wgPageContentLanguage":"en","wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"dmy","wgMonthNames":["","January","February","March","April","May","June","July","August","September","October","November","December"],"wgMonthNamesShort":["","Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"],"wgRelevantPageName":"c/language/struct_initialization","wgRestrictionEdit":[],"wgRestrictionMove":[]});
}</script><script>if(window.mw){
mw.loader.implement("user.options",function(){mw.user.options.set({"ccmeonemails":0,"cols":80,"date":"default","diffonly":0,"disablemail":0,"disablesuggest":0,"editfont":"default","editondblclick":0,"editsection":0,"editsectiononrightclick":0,"enotifminoredits":0,"enotifrevealaddr":0,"enotifusertalkpages":1,"enotifwatchlistpages":0,"extendwatchlist":0,"externaldiff":0,"externaleditor":0,"fancysig":0,"forceeditsummary":0,"gender":"unknown","hideminor":0,"hidepatrolled":0,"imagesize":2,"justify":0,"math":1,"minordefault":0,"newpageshidepatrolled":0,"nocache":0,"noconvertlink":0,"norollbackdiff":0,"numberheadings":0,"previewonfirst":0,"previewontop":1,"quickbar":5,"rcdays":7,"rclimit":50,"rememberpassword":0,"rows":25,"searchlimit":20,"showhiddencats":0,"showjumplinks":1,"shownumberswatching":1,"showtoc":0,"showtoolbar":1,"skin":"cppreference2","stubthreshold":0,"thumbsize":2,"underline":2,"uselivepreview":0,"usenewrc":0,"watchcreations":0,"watchdefault":0,"watchdeletion":0,
"watchlistdays":3,"watchlisthideanons":0,"watchlisthidebots":0,"watchlisthideliu":0,"watchlisthideminor":0,"watchlisthideown":0,"watchlisthidepatrolled":0,"watchmoves":0,"wllimit":250,"variant":"en","language":"en","searchNs0":true,"searchNs1":false,"searchNs2":false,"searchNs3":false,"searchNs4":false,"searchNs5":false,"searchNs6":false,"searchNs7":false,"searchNs8":false,"searchNs9":false,"searchNs10":false,"searchNs11":false,"searchNs12":false,"searchNs13":false,"searchNs14":false,"searchNs15":false,"gadget-ColiruCompiler":1});;},{},{});mw.loader.implement("user.tokens",function(){mw.user.tokens.set({"editToken":"+\\","patrolToken":false,"watchToken":false});;},{},{});
/* cache key: mwiki1-mwiki_en_:resourceloader:filter:minify-js:7:ca03345b1e2c4d90a25d968753a73b92 */
}</script>
<script>if(window.mw){
mw.loader.load(["mediawiki.page.startup","mediawiki.legacy.wikibits","mediawiki.legacy.ajax"]);
}</script>
<style type="text/css">/*<![CDATA[*/
.source-c {line-height: normal;}
.source-c li, .source-c pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for c
 * CSS class: source-c, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.c.source-c .de1, .c.source-c .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.c.source-c  {font-family:monospace;}
.c.source-c .imp {font-weight: bold; color: red;}
.c.source-c li, .c.source-c .li1 {font-weight: normal; vertical-align:top;}
.c.source-c .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.c.source-c .li2 {font-weight: bold; vertical-align:top;}
.c.source-c .kw1 {color: #0000dd;}
.c.source-c .kw2 {color: #0000ff;}
.c.source-c .kw3 {color: #0000dd;}
.c.source-c .kw4 {color: #0000ff;}
.c.source-c .co1 {color: #909090;}
.c.source-c .co2 {color: #339900;}
.c.source-c .coMULTI {color: #ff0000; font-style: italic;}
.c.source-c .es0 {color: #008000; font-weight: bold;}
.c.source-c .es1 {color: #008000; font-weight: bold;}
.c.source-c .es2 {color: #008000; font-weight: bold;}
.c.source-c .es3 {color: #008000; font-weight: bold;}
.c.source-c .es4 {color: #008000; font-weight: bold;}
.c.source-c .es5 {color: #008000; font-weight: bold;}
.c.source-c .br0 {color: #008000;}
.c.source-c .sy0 {color: #008000;}
.c.source-c .sy1 {color: #000080;}
.c.source-c .sy2 {color: #000040;}
.c.source-c .sy3 {color: #000040;}
.c.source-c .sy4 {color: #008080;}
.c.source-c .st0 {color: #008000;}
.c.source-c .nu0 {color: #000080;}
.c.source-c .nu6 {color:#000080;}
.c.source-c .nu8 {color:#000080;}
.c.source-c .nu12 {color:#000080;}
.c.source-c .nu16 {color:#000080;}
.c.source-c .nu17 {color:#000080;}
.c.source-c .nu18 {color:#000080;}
.c.source-c .nu19 {color:#000080;}
.c.source-c .ln-xtra, .c.source-c li.ln-xtra, .c.source-c div.ln-xtra {background-color: #ffc;}
.c.source-c span.xtra { display:block; }

/*]]>*/
</style>
<style type="text/css">/*<![CDATA[*/
.source-text {line-height: normal;}
.source-text li, .source-text pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for text
 * CSS class: source-text, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.text.source-text .de1, .text.source-text .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.text.source-text  {font-family:monospace;}
.text.source-text .imp {font-weight: bold; color: red;}
.text.source-text li, .text.source-text .li1 {font-weight: normal; vertical-align:top;}
.text.source-text .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.text.source-text .li2 {font-weight: bold; vertical-align:top;}
.text.source-text .ln-xtra, .text.source-text li.ln-xtra, .text.source-text div.ln-xtra {background-color: #ffc;}
.text.source-text span.xtra { display:block; }

/*]]>*/
</style>
<!--[if lt IE 7]><style type="text/css">body{behavior:url("/mwiki/skins/cppreference2/csshover.min.htc")}</style><![endif]-->
</head>
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_language_struct_initialization skin-cppreference2 action-view cpp-navbar">
        <!-- header -->
        
        <!-- /header -->
        <!-- content -->
        <div id="cpp-content-base">
            <div id="content">
                <a id="top"></a>
                <div id="mw-js-message" style="display:none;"></div>
                                <!-- firstHeading -->
                <h1 id="firstHeading" class="firstHeading">Struct and union initialization</h1>
                <!-- /firstHeading -->
                <!-- bodyContent -->
                <div id="bodyContent">
                                        <!-- tagline -->
                    <div id="siteSub">From cppreference.com</div>
                    <!-- /tagline -->
                                        <!-- subtitle -->
                    <div id="contentSub"><span class="subpages">&lt; <a href="../../c.html" title="c">c</a>‎ | <a href="../language.1.html" title="c/language">language</a></span></div>
                    <!-- /subtitle -->
                                                            <!-- bodycontent -->
                    <div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr">
<div class="t-navbar" style="">
<div class="t-navbar-sep"> </div>
<div class="t-navbar-head">
<a href="../../c.html" title="c"> C</a><div class="t-navbar-menu"><div>
<div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
<tr class="t-nv"><td colspan="5"> <a href="../language.1.html" title="c/language"> Language</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../header.html" title="c/header"> headers</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../types.html" title="c/types"> Type support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../memory.html" title="c/memory"> Dynamic memory management</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../error.html" title="c/error"> Error handling</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../program.html" title="c/program"> Program utilities</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../variadic.html" title="c/variadic"> Variadic function support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../chrono.html" title="c/chrono"> Date and time utilities</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../string.html" title="c/string"> Strings library</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../algorithm.html" title="c/algorithm"> Algorithms</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../numeric.html" title="c/numeric"> Numerics</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../io.html" title="c/io"> Input/output support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../locale.html" title="c/locale"> Localization support</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../thread.html" title="c/thread"> Thread support</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../atomic.html" title="c/atomic"> Atomic operations</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../experimental.html" title="c/experimental"><span class="t-lines"><span>Technical Specifications</span></span></a></div></div></td></tr>
</table></div>
<div></div>
</div></div>
</div>
<div class="t-navbar-sep"> </div>
<div class="t-navbar-head">
<a href="../language.1.html" title="c/language"> C language</a><div class="t-navbar-menu"><div>
<div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="ascii.html" title="c/language/ascii"><span class="t-lines"><span>ASCII chart</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="basic_concepts.html" title="c/language/basic concepts">Basic concepts</a>
</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="translation_phases.html" title="c/language/translation phases"><span class="t-lines"><span>translation phases</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../comment.html" title="c/comment"><span class="t-lines"><span>comment</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="identifier.html" title="c/language/identifier"><span class="t-lines"><span>identifier</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="scope.html" title="c/language/scope"><span class="t-lines"><span>scope</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="lifetime.html" title="c/language/lifetime"><span class="t-lines"><span>lifetime</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="name_space.html" title="c/language/name space"><span class="t-lines"><span>name space</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="compatible_type.html" title="c/language/type"><span class="t-lines"><span>type</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="arithmetic_types.html" title="c/language/arithmetic types"><span class="t-lines"><span>arithmetic types</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="object.html" title="c/language/object"><span class="t-lines"><span>object</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="main_function.html" title="c/language/main function"><span class="t-lines"><span>main function</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="memory_model.html" title="c/language/memory model"><span class="t-lines"><span>memory model</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../keyword.html" title="c/keyword"> Keywords</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../preprocessor.html" title="c/preprocessor"> Preprocessor</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="statements.html" title="c/language/statements"> Statements</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="expressions.html" title="c/language/expressions"> Expressions</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="initialization.html" title="c/language/initialization"> Initialization</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="declarations.html" title="c/language/declarations"> Declarations</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="functions.html" title="c/language/functions"> Functions</a>
</td></tr>
<tr class="t-nv-h2"><td colspan="5"> Miscellaneous</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="history.html" title="c/language/history"><span class="t-lines"><span>history of C</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../experimental.html" title="c/experimental">Technical Specifications</a> </td></tr>
</table></div>
<div></div>
</div></div>
</div>
<div class="t-navbar-sep"> </div>
<div class="t-navbar-head">
<a href="initialization.html" title="c/language/initialization"> Initialization</a><div class="t-navbar-menu"><div>
<div style="display:inline-block">
<div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="initialization.html#Explicit_initialization" title="c/language/initialization"><span class="t-lines"><span>explicit initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="initialization.html#Implicit_initialization" title="c/language/initialization"><span class="t-lines"><span>implicit initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="scalar_initialization.html" title="c/language/scalar initialization"><span class="t-lines"><span>scalar initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="array_initialization.html" title="c/language/array initialization"><span class="t-lines"><span>array initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><strong class="selflink"><span class="t-lines"><span>struct and union initialization</span></span></strong></div></div></td></tr>
</table></div>
</div>
<div></div>
</div></div>
</div>
<div class="t-navbar-sep"> </div>
</div>
<p>When <a href="initialization.html" title="c/language/initialization">initializing</a> an object of <a href="struct.html" title="c/language/struct">struct</a> or <a href="union.html" title="c/language/union">union</a> type, the initializer must be a non-empty, brace-enclosed, comma-separated list of initializers for the members:
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td>
</tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <code><b>=</b></code> <code><b>{ </b></code> <span class="t-spar">designator</span><span class="t-mark">(optional)</span> <span class="t-spar">expression</span> <code><b>,</b></code> <code><b>...</b></code> <code><b>} </b></code>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td>
</tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td>
</tr>
</table>
<p>where the <span class="t-spar">designator</span> is a sequence (whitespace-separated or adjacent) of individual member designators of the form <code><b>.</b></code> <span class="t-spar">member</span> and <a href="array_initialization.html" title="c/language/array initialization">array designators</a> of the form <code><b>[</b></code> <span class="t-spar">index</span> <code><b>]</b></code>.
</p>
<p>All members that are not initialized explicitly are <a href="initialization.html#Implicit_initialization" title="c/language/initialization">initialized implicitly</a> the same way as objects that have static storage duration.
</p>
<table id="toc" class="toc"><tr><td>
<div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="struct_initialization.html#Explanation"><span class="tocnumber">1</span> <span class="toctext">Explanation</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="struct_initialization.html#Nested_initialization"><span class="tocnumber">2</span> <span class="toctext">Nested initialization</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="struct_initialization.html#Notes"><span class="tocnumber">3</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="struct_initialization.html#Example"><span class="tocnumber">4</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="struct_initialization.html#References"><span class="tocnumber">5</span> <span class="toctext">References</span></a></li>
</ul>
</td></tr></table>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span>
</h3>
<p>When initializing a <a href="union.html" title="c/language/union">union</a>, the initializer list must have only one member, which initializes the first member of the union<span class="t-rev-inl t-since-c99"><span> unless a designated initializer is used</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">union</span> <span class="br0">{</span> <span class="kw4">int</span> x<span class="sy4">;</span> <span class="kw4">char</span> c<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span> <span class="br0">}</span>
  u <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span>,           <span class="co1">// makes u.x active with value 1</span>
 u2 <span class="sy1">=</span> <span class="br0">{</span> .<span class="me1">c</span><span class="sy1">=</span><span class="br0">{</span><span class="st0">'<span class="es5">\1</span>'</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// makes u2.c active with value {'\1','\0','\0','\0'}</span></pre></div></div>
<p>When initializing a <a href="struct.html" title="c/language/struct">struct</a>, the first initializer in the list initializes the first declared member<span class="t-rev-inl t-since-c99"><span> (unless a designator is specified)</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>, and all subsequent initializers <span class="t-rev-inl t-since-c99"><span>without designators </span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>initialize the struct members declared after the one initialized by the previous expression.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> point <span class="br0">{</span><span class="kw4">double</span> x,y,z<span class="sy4">;</span><span class="br0">}</span> p <span class="sy1">=</span> <span class="br0">{</span><span class="nu16">1.2</span>, <span class="nu16">1.3</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// p.x=1.2, p.y=1.3, p.z=0.0</span>
div_t answer <span class="sy1">=</span> <span class="br0">{</span>.<span class="me1">quot</span> <span class="sy1">=</span> <span class="nu0">2</span>, .<span class="me1">rem</span> <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span> <span class="br0">}</span><span class="sy4">;</span>      <span class="co1">// order of elements in div_t may vary</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99">
<td>
<p>A designator causes the following initializer to initialize the struct member described by the designator. Initialization then continues forward in order of declaration, beginning with the next element declared after the one described by the designator.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> sec,min,hour,day,mon,year<span class="sy4">;</span><span class="br0">}</span> z
   <span class="sy1">=</span> <span class="br0">{</span>.<span class="me1">day</span><span class="sy1">=</span><span class="nu0">31</span>,<span class="nu0">12</span>,<span class="nu0">2014</span>,.<span class="me1">sec</span><span class="sy1">=</span><span class="nu0">30</span>,<span class="nu0">15</span>,<span class="nu0">17</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// initializes z to {30,15,17,31,12,2014}</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td>
</tr>
</table>
<p>It's an error to provide more initializers than members.
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Nested initialization">edit</a>]</span> <span class="mw-headline" id="Nested_initialization">Nested initialization</span>
</h3>
<p>If the members of the struct or union are arrays, structs, or unions, the corresponding initializers in the brace-enclosed list of initializers are any initializers that are valid for those members, except that their braces may be omitted as follows:
</p>
<p>If the nested initializer begins with an opening brace, the entire nested initializer up to its closing brace initializes the corresponding member object. Each left opening brace establishes a new <i>current object</i>. The members of the current object are initialized in their natural order<span class="t-rev-inl t-since-c99"><span>, unless designators are used</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>: array elements in subscript order, struct members in declaration order, only the first declared member of any union. The subobjects within the current object that aren't explicitly initialized by the closing brace are <a href="initialization.html#Implicit_initialization" title="c/language/initialization">implicitly initialized</a>.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> example <span class="br0">{</span>
    <span class="kw1">struct</span> addr_t <span class="br0">{</span>
       <a href="../types/integer.html"><span class="kw122">uint32_t</span></a> port<span class="sy4">;</span>
    <span class="br0">}</span> addr<span class="sy4">;</span>
    <span class="kw1">union</span> <span class="br0">{</span>
       <a href="../types/integer.html"><span class="kw120">uint8_t</span></a> a8<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span>
       <a href="../types/integer.html"><span class="kw121">uint16_t</span></a> a16<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span>
    <span class="br0">}</span> in_u<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> example ex <span class="sy1">=</span> <span class="br0">{</span> <span class="co1">// start of initializer list for struct example</span>
                     <span class="br0">{</span> <span class="co1">// start of initializer list for ex.addr</span>
                        <span class="nu0">80</span> <span class="co1">// initialized struct's only member</span>
                     <span class="br0">}</span>, <span class="co1">// end of initializer list for ex.addr</span>
                     <span class="br0">{</span> <span class="co1">// start of initializer-list for ex.in_u</span>
                        <span class="br0">{</span><span class="nu0">127</span>,<span class="nu0">0</span>,<span class="nu0">0</span>,<span class="nu0">1</span><span class="br0">}</span> <span class="co1">// initializes first element of the union</span>
                     <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>If the nested initializer does not begin with an opening brace, only enough initializers from the list are taken to account for the elements or members of the member array, struct or union; any remaining initializers are left to initialize the next struct member:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> example ex <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">80</span>, <span class="nu0">127</span>, <span class="nu0">0</span>, <span class="nu0">0</span>, <span class="nu0">1</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 80 initializes ex.addr.port</span>
                                        <span class="co1">// 127 initializes ex.in_u.a8[0]</span>
                                        <span class="co1">// 0 initializes ex.in_u.a8[1]</span>
                                        <span class="co1">// 0 initializes ex.in_u.a8[2]</span>
                                        <span class="co1">// 1 initializes ex.in_u.a8[3]</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99">
<td>
<p>When designators are nested, the designators for the members follow the designators for the enclosing structs/unions/arrays. Within any nested bracketed initializer list, the outermost designator refers to the <i>current object</i> and selects the subobject to be initialized within the <i>current object</i> only.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> example ex2 <span class="sy1">=</span> <span class="br0">{</span> <span class="co1">// current object is ex2, designators are for members of example</span>
                       .<span class="me1">in_u</span>.<span class="me1">a8</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="sy1">=</span><span class="nu0">127</span>, <span class="nu0">0</span>, <span class="nu0">0</span>, <span class="nu0">1</span>, .<span class="me1">addr</span><span class="sy1">=</span><span class="nu0">80</span><span class="br0">}</span><span class="sy4">;</span> 
<span class="kw1">struct</span> example ex3 <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">80</span>, .<span class="me1">in_u</span><span class="sy1">=</span><span class="br0">{</span> <span class="co1">// changes current object to the union ex.in_u</span>
                           <span class="nu0">127</span>,
                           .<span class="me1">a8</span><span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy1">=</span><span class="nu0">1</span> <span class="co1">// this designator refers to the member of in_u</span>
                      <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>If any subobject is explicitly initialized twice (which may happen when designators are used), the initializer that appears later in the list is the one used (the earlier initializer may not be evaluated):
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> n<span class="sy4">;</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"a<span class="es1">\n</span>"</span><span class="br0">)</span>, <span class="co1">// this may be printed or skipped</span>
                     .<span class="me1">n</span><span class="sy1">=</span><a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"b<span class="es1">\n</span>"</span><span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// always printed</span></pre></div></div>
<p>Although any non-initialized subobjects are initialized implicitly, implicit initialization of a subobject never overrides explicit initialization of the same subobject if it appeared earlier in the initializer list:
</p>
<div class="t-example">
<div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="kw1">typedef</span> <span class="kw1">struct</span> <span class="br0">{</span> <span class="kw4">int</span> k<span class="sy4">;</span> <span class="kw4">int</span> l<span class="sy4">;</span> <span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span> <span class="br0">}</span> T<span class="sy4">;</span>
<span class="kw1">typedef</span> <span class="kw1">struct</span> <span class="br0">{</span> <span class="kw4">int</span> i<span class="sy4">;</span>  T t<span class="sy4">;</span> <span class="br0">}</span> S<span class="sy4">;</span>
T x <span class="sy1">=</span> <span class="br0">{</span>.<span class="me1">l</span> <span class="sy1">=</span> <span class="nu0">43</span>, .<span class="me1">k</span> <span class="sy1">=</span> <span class="nu0">42</span>, .<span class="me1">a</span><span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">19</span>, .<span class="me1">a</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">18</span> <span class="br0">}</span><span class="sy4">;</span>
 <span class="co1">// x initialized to {42, 43, {18, 19} }</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    S l <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">1</span>,          <span class="co1">// initializes l.i to 1</span>
           .<span class="me1">t</span> <span class="sy1">=</span> x,      <span class="co1">// initializes l.t to {42, 43, {18, 19} }</span>
           .<span class="me1">t</span>.<span class="me1">l</span> <span class="sy1">=</span> <span class="nu0">41</span>,   <span class="co1">// changes l.t to {42, 41, {18, 19} }</span>
           .<span class="me1">t</span>.<span class="me1">a</span><span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">17</span> <span class="co1">// changes l.t to {42, 41, {18, 17} }</span>
          <span class="br0">}</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"l.t.k is %d<span class="es1">\n</span>"</span>, l.<span class="me1">t</span>.<span class="me1">k</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// .t = x sets l.t.k to 42 explicitly</span>
                                    <span class="co1">// .t.l = 42 would zero out l.t.k implicitly</span>
<span class="br0">}</span></pre></div></div>
<p>Output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">l.t.k is 42</pre></div></div> 
</div>
<p>However, when an initializer begins with a left open brace, its <i>current object</i> is fully re-initialized and any prior explicit initializers for any of its subobjects are ignored:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> fred <span class="br0">{</span> <span class="kw4">char</span> s<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span> <span class="kw4">int</span> n<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> fred x<span class="br0">[</span> <span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"abc"</span> <span class="br0">}</span>, <span class="nu0">1</span> <span class="br0">}</span>, <span class="co1">// inits x[0] to { {'a','b','c','\0'}, 1 }</span>
                      <span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>.<span class="me1">s</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">'q'</span>   <span class="co1">// changes x[0] to { {'q','b','c','\0'}, 1 }</span>
                   <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> fred y<span class="br0">[</span> <span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"abc"</span> <span class="br0">}</span>, <span class="nu0">1</span> <span class="br0">}</span>, <span class="co1">// inits x[0] to { {'a','b','c','\0'}, 1 }</span>
                     <span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="co1">// current object is now the entire x[0] object</span>
                             .<span class="me1">s</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">'q'</span> 
                            <span class="br0">}</span> <span class="co1">// replaces x[0] with { {'q','\0','\0','\0'}, 0 }</span>
                    <span class="br0">}</span><span class="sy4">;</span></pre></div></div> 
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td>
</tr>
</table>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span>
</h3>
<p>The <a href="eval_order.html" title="c/language/eval order">order of evaluation</a> of the subexpressions in any initializer is indeterminately sequenced:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> x,y<span class="sy4">;</span><span class="br0">}</span> p <span class="sy1">=</span> <span class="br0">{</span>n<span class="sy2">++</span>, n<span class="sy2">++</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// unspecified, but well-defined behavior:</span>
                                  <span class="co1">// n is incremented twice in arbitrary order</span>
                                  <span class="co1">// p equal {1,2} and {2,1} are both valid</span></pre></div></div>
<p>In C, the braced list of initializers cannot be empty (note that C++ allows empty lists, and also note that a <a href="struct.html" title="c/language/struct">struct</a> in C cannot be empty):
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> n<span class="sy4">;</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">0</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// OK</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> n<span class="sy4">;</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// Error: initializer-list cannot be empty</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// Error: struct cannot be empty, initializer-list cannot be empty</span></pre></div></div>
<p>As with all other <a href="initialization.html" title="c/language/initialization">initialization</a>, every expression in the initializer list must be a <a href="constant_expression.html" title="c/language/constant expression">constant expression</a> when initializing arrays of static or thread-local <a href="storage_duration.html" title="c/language/storage duration">storage duration</a>:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">static</span> <span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">char</span><span class="sy2">*</span> p<span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><a href="../memory/malloc.html"><span class="kw403">malloc</span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// error</span></pre></div></div>
<p>The initializer list may have a trailing comma, which is ignored.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">double</span> x,y<span class="sy4">;</span><span class="br0">}</span> p <span class="sy1">=</span> <span class="br0">{</span><span class="nu16">1.0</span>,
                          <span class="nu16">2.0</span>, <span class="co1">// trailing comma OK</span>
                          <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p><br>
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span>
</h3>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr>
<td class="mbox-empty-cell"></td>
<td class="mbox-text" style="">This section is incomplete<br>Reason: more practical examples, perhaps initialize some socket structs </td>
</tr></table>
<div class="t-example">
<div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;time.h&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">char</span> buff<span class="br0">[</span><span class="nu0">70</span><span class="br0">]</span><span class="sy4">;</span>
    <span class="co1">// designated initalizers simplify the use of structs whose</span>
    <span class="co1">// order of members is unspecified</span>
    <span class="kw1">struct</span> <a href="../chrono/tm.html"><span class="kw523">tm</span></a> my_time <span class="sy1">=</span> <span class="br0">{</span> .<span class="me1">tm_year</span><span class="sy1">=</span><span class="nu0">112</span>, .<span class="me1">tm_mon</span><span class="sy1">=</span><span class="nu0">9</span>, .<span class="me1">tm_mday</span><span class="sy1">=</span><span class="nu0">9</span>,
                          .<span class="me1">tm_hour</span><span class="sy1">=</span><span class="nu0">8</span>, .<span class="me1">tm_min</span><span class="sy1">=</span><span class="nu0">10</span>, .<span class="me1">tm_sec</span><span class="sy1">=</span><span class="nu0">20</span> <span class="br0">}</span><span class="sy4">;</span>
    <a href="../chrono/strftime.html"><span class="kw517">strftime</span></a><span class="br0">(</span>buff, <span class="kw4">sizeof</span> buff, <span class="st0">"%A %c"</span>, <span class="sy3">&amp;</span>my_time<span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span>buff<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Possible output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">Sunday Sun Oct  9 08:10:20 2012</pre></div></div> 
</div>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: References">edit</a>]</span> <span class="mw-headline" id="References">References</span>
</h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd>
<ul><li> 6.7.9/12-38 Initialization (p: 140-144)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd>
<ul><li> 6.7.8/12-38 Initialization (p: 126-130)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd>
<ul><li> 3.5.7/9- Initialization 
</li></ul>
</dd></dl>
</div>
</div>
</div>

<!-- 
NewPP limit report
Preprocessor visited node count: 2542/1000000
Preprocessor generated node count: 7934/1000000
Post‐expand include size: 54447/2097152 bytes
Template argument size: 15339/2097152 bytes
Highest expansion depth: 17/40
Expensive parser function count: 0/100
-->

<!-- Saved in parser cache with key mwiki1-mwiki_en_:pcache:idhash:13916-0!*!0!!en!*!* and timestamp 20150623113559 -->
</div>                    <!-- /bodycontent -->
                                        <!-- printfooter -->
                    <div class="printfooter">
                    Retrieved from "<a href="http%3A//en.cppreference.com/mwiki/index.php">http://en.cppreference.com/mwiki/index.php?title=c/language/struct_initialization&amp;oldid=79096</a>"                    </div>
                    <!-- /printfooter -->
                                                            <!-- catlinks -->
                    <div id="catlinks" class="catlinks"><div id="mw-normal-catlinks" class="mw-normal-catlinks">
<a href="http%3A//en.cppreference.com/w/Special%3ACategories" title="Special:Categories">Category</a>: <ul><li><a href="http%3A//en.cppreference.com/w/Category%3ATodo_with_reason" title="Category:Todo with reason">Todo with reason</a></li></ul>
</div></div>                    <!-- /catlinks -->
                                                            <div class="visualClear"></div>
                    <!-- debughtml -->
                                        <!-- /debughtml -->
                </div>
                <!-- /bodyContent -->
            </div>
        </div>
        <!-- /content -->
        <!-- footer -->
        
        <!-- /footer -->
        <script>if(window.mw){
mw.loader.state({"site":"loading","user":"missing","user.groups":"ready"});
}</script>
<script src="../../../common/skin_scripts.js"></script>
<script>if(window.mw){
mw.loader.load(["mediawiki.action.view.postEdit","mediawiki.user","mediawiki.page.ready","mediawiki.searchSuggest","mediawiki.hidpi","ext.gadget.ColiruCompiler"], null, true);
}</script>
<script src="../../../common/site_scripts.js"></script>

<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-2828341-1']);
_gaq.push(['_setDomainName', 'cppreference.com']);
_gaq.push(['_trackPageview']);
</script><!-- Served in 0.089 secs. -->
	</body>
<!-- Cached 20150623113921 -->
</html>
